Method of and apparatus for sorting crystals according to size

ABSTRACT

A device for sorting crystals according to their size comprises a separation chamber divided into two parts; a fluid carrying the crystals to be sorted passes into a first of these parts while a separate driving fluid is passed into the second, the flow-rate of fluid passing out of the second part being less than the flowrate of driving fluid which passes into the second part, while the flow-rate of fluid passing out of the first part is higher than the flow-rate of carrier fluid passing into the first part, whereby at least a portion of the driving fluid passes across an interface separating the two parts, in counter-flow to the largest crystals to be sorted; the crystals to be sorted tend to flow from the first part to the second but the upward speed of the driving fluid in the separation chamber prevents such flow except for the crystals having the desired diameter, regulated by the speed of the fluid.

United States Patent Laurenty [451 Sept. 5, 1972 [72] Inventor: FrancoisLaurenty, Le Touquet,

France [73] Assignee: C.O.C.E.I. SA, Paris, France; a part interest [22]Filed: Nov. 10, 1969 [21] App1.No.: 875,096

[30] Foreign Application Priority Data Nov. 15, 1968 France 173.845

[52] US. Cl. ..209/l57, 209/155, 209/158, 209/21 1 [51] Int. Cl. ..B03b3/30 [58] Field otSearch ..209/l55161; 23/273 [56] References CitedUNITED STATES PATENTS 118,379 8/1871 Merrill ..209/l60 1,177,849 4/1916De Kalb ..209/l60 X 3,219,186 11/1965 Polhemus et a]. ......209/172.53,295,677 1/1967 Condolios ..209/158 X FOREIGN PATENTS OR APPLICATIONS987,908 3/ 1965 Great Britain ..209/ 158 Primary Examiner-Frank W.Lutter Assistant Examiner-Ralph J. Hill Attorney-Young & Thompson [57]ABSTRACT A device for sorting crystals according to their size comprisesa separation chamber divided into two parts; a fluid carrying thecrystals to be sorted passes into a first of these parts while aseparate driving fluid is passed into the second, the flow-rate of fluidpassing out of the second part being less than the flow-rate of drivingfluid which passes into the second part, while the flow-rate of fluidpassing out of the first part is higher than the flow-rate of carrierfluidpassing into the first part, whereby at least a portion of thedriving fluid passes across an interface separating the two parts, incounter-flow to the largest crystals to be sorted; the crystals to besorted tend to flow from the first part to the second but the upwardspeed of the driving fluid in the separation chamber prevents such flowexcept for the crystals having the desired diameter, regulated by thespeed of the fluid.

8 Claims, 16 Drawing Figures Patented Sept. 5, 1972 2 Sheets-Sheet 2 FIG12 METHOD OF AND APPARATUS FOR SORTING CRYSTALS ACCORDING TO SIZE Thepresent invention has for its object a method of and a device foreffecting the sorting of crystals, carried by a fluid of differentdensity, according to their size, and is especially directed to theapplication of such a device to a crystallization installation.

A crystallization installation comprises, in a manner known per se, acrystallization circuit such as an evaporation circuit or a coolingcircuit, and a circuit for removing excess liquid, and generallydelivers crystals having a granular size distributed over an extensiverange of diameters, from the finest to the largest, according to theusual laws of statistics in this matter.

Now, as is well known, it is of the greatest advantage to obtaincrystals in which the granulometric distribution is as narrow aspossible on each side of a welldefined mean diameter.

The method and the device forming the objects of the present inventionachieve this purpose; they further enable the diameter of the crystalsobtained to be regulated at will.

The invention provides for the utilization of a separation chamberhaving two parts, between which exists a force field, the said partscomprising a common interface and being each provided with a fluid inletand outlet, in combination with regulating means permitting thevariation of any one of the following parameters: useful area of theinterface, flow-rate passing through this interface, intensity of theforce field.

According to a static form of embodiment, that is to say according to aform of construction which only comprises static members, the separationchamber of the device according to the invention is confined in a tanksubjected only to the force field, and divided into two parts byadjustable throttling means which enable the flow-rate of fluid from oneof the said parts to the other to be modulated at will.

In an alternative embodiment, according to a dynamis form ofconstruction, the separation chamber is ar ranged downstream of a smallwheel rotatably mounted in a fixed cylindrical chamber, this wheelensuring the setting in rotation of the fluids which pass into the twoparts of the said volume, so that in this latter, the said fluids aresubjected to a centrifugal force field different from the normal forcefield and generally higher than this normal field.

However this may be, the separation chamber receives, according to theinvention, two fluids which are hereinafter known, for convenience ofthe description, as the driving fluid or fluid A, and the carrier fluidor fluid B. The crystals to be sorted, carried by the fluid B pass intoa first of the parts of the separation chamber and are subjected in thischamber to a force field; they thus tend to flow from this first part ofthe said chamber to the second. Conjointly, in this second part of theseparation chamber passes the fluid A, of which at least a portion tendsto pass from this second part to the first across the interface. Theresulting flow-rate of fluid across this interface opposes the flowreferred to above of the crystals to be sorted or classified, so thatonly the crystals having a sufficient diameter effectively flow across.

The method and the device according to the invention resultadvantageously in simple and effective constructions which can veryreadily be added to any previously existing crystallizationinstallation. For that purpose, it is only necessary to place the deviceaccording to the invention in shunt on the one hand with theconcentration circuit and on the other hand with the excessliquid-removal circuit of such a crystallization installation.

When this has been done, by virtue of the device according to theinvention, the too-fine crystals are re-cycled while the too-largecrystals can either be sieved in the excess liquid removal circuit orelsewhere, or reduced to smaller dimensions, by crushing for example.

By this means, the installation only delivers crystals of well-defineddimensions.

The characteristic features and advantages of the invention will befurther brought out in the description which follows below, given by wayof example only, reference being made to the accompanying diagrammaticdrawings, in which:

FIG. I is a perspective view with parts broken away, of a deviceaccording to the invention;

FIG. 2 is a diagram illustrating the inclusion of this device in acrystallization installation;

FIG. 3 is a diagrammatic view in elevation, illustrating the operationof this device;

FIGS. 4A, 4B and 4C are partial views which relate to one of theelements utilized in the device according to the invention, and whicheach illustrate one form of construction of this element;

FIG. 4D is a view in cross-section of the form of construction shown inFIG. 4C, taken along the line D-D of this figure;

FIG. 5 is a perspective view similar to FIG. I, and relates to analternative construction of the device ac cording to the invention;

FIG. 6 is a perspective view illustrating the combination in parallel ofa plurality of devices according to the invention;

FIG. 7 is a view in axial section of an alternative form of constructionof the device according to the invention, employing a small rotatingwheel;

FIGS. 8 and 9 are views in transverse section of the construction shownin FIG. '7, taken respectively along the lines VIII-VIII and IX-IX ofFIG. 7;

FIG. 10 is a view similar to FIG. 8 and relates to an alternative formof construction;

FIGS. 11 to 13 are views similar to FIG. 7, and each relates to anotheralternative form of construction.

In accordance with the form of embodiment chosen and shown in FIG. 1,the device according to the invention comprises a tank 10 of generallyparallelepiped shape, the internal space of which constitutes theseparation chamber V according to the invention. This chamber is dividedhorizontally into two parts, a lower part HA and an upper part 11B, byadjustable throttling shutters 13, the actuation of which will bedescribed in detail later, and which more or less intercept the passageof fluid from the lower part 11A to the upper part 1 1B of this volume.

The lower part 11A of the tank 10 is provided with a fluid-inlet 14A anda fluid-outlet 15A located in the extension of that preceding.Similarly, the upper part I I8 of the tank comprises an inlet 14B and anoutlet 158 which, in the example shown, are respectively parallel to theinlet 14A and to the outlet 15A of the lower part 1 1A.

Reference will now be made to FIG. 2, in which a cryatallizationinstallation has been shown diagrammatically.

An installation of this kind generally comprises a crystallization body20, such as an evaporator or cooler.

As shown in heavy lines in FIG. 2, the 'outlet 21 of this body iscoupled to the inlet 14B of the tank 10 of the device according to theinvention, while the outlet 158 of this tank is connected to the supply22 of the body 20, through the intermediary of a pump 23.

Furthermore, the tank 10 is also included by its inlet 14A and itsoutlet 15A in an excess liquid removal circuit 30 comprising for examplea centrifuge 31 and a circulation pump 32.

In an installation of this kind, the introduction of the fresh liquor,non-saturated but rich in dissolved product and therefore dense, can beeffected for example in the centrifuge dryer, as indicated by the arrow35 in broken lines, or alternatively it can be made at any point of thedrying circuit 30 as indicated by the arrow 36 in full lines.

With regard to the extraction of exhausted liquor, this can be done atany appropriate point of the circulation circuit 25, as showndiagrammatically by the arrow 37, or alternatively at any suitable pointof the crystallization body 20.

Reference will now be made to FIG. 3, which is a simple diagramrepresenting the device according to the invention.

A liquor B arrives at 14B containing the crystals which have been formedor which have been increased in size in the crystallization body 20. Thedensity of this liquor is obviously less than that of the crystals.

Due to the effect of gravity alone, the crystals carried by this liquorB have therefore a tendency to settle in the tank 10.

A liquor A arrives at 14A coming from the drying circuit; this liquor iscomposed on the one hand of the liquid volume which travels in a closedcircuit in this drying circuit, and on the other hand, of theunsaturated liquid volume introduced either at 35 or at 36. The densityof this liquor A is higher than that of the liquor B but is still lessthan that of the crystals. Thus the liquors A and B define a range ofdensities which excludes that of the crystals, that is, the density ofthe crystals lies outside the range of densities of the liquids.

The flow-rate of liquor A passing out at 15A is made smaller than theflow-rate passing in at 14A; conjointly the flow passing out at 158 ismade higher than the flow-rate of liquor B passing in at 14B. There istherefore an upward flow of liquor A in the tank 10 in the direction ofthe arrow 40 of FIG. 3, this upward flow taking place in the directionopposite to that along which the crystals passing into 148 have atendency to flow into the tank 10.

In consequence, by regulating the upward speed of this flow, it ispossible to effect a choice between the crystals, some of these crystalsbeing effectively able to flow through while others are prevented fromflowing through.

This selection is made as a function of the speed of flow of thecrystals with respect to this upward speed of the liquor A in the tank10, and in consequence as a function of the diameter of these crystals,the other conditions, such as viscosity in particular, being assumed tobe the same.

Thus, a liquor passes out at 158 which has lost its lar gest crystals,these crystals being found on the other hand in the liquor which passesout at 15A.

Everything takes place as if in the tank Ill there existed an interface8 between the liquor B passing in at 148 and the liquor A passing in at14A, and as if there were a transfer of crystals from one liquor to theother across this interface, as a function of the diameter of the saidcrystals.

In FIG. 3, this interface S has been arbitrarily represented by a brokenline at the level of the shutters 13.

However this may be, the liquor which passes out at 15A and which issent to the dryer comprises only crystals having a diameter greater thana given diameter which is a function of the upward speed of the liquorin the tank 10.

In order to vary this diameter, it is thus only necessary to modify thisupward speed.

This modification of speed can be effected in two ways:

either, the area of the interface S between the parts 11A and 11B of thetank 10 remaining equal, by modifying the flow-rate of the liquorintroduced into the tank 10, or in a more general manner, the differenceof flow-rate between the flow passing-in at 14A and the flow passing-outat 15A;

or, this flow-rate or this difference in flow-rate remaining equal, bymodifying this section by acting on the throttling shutters 13.

To this end, and as shown by way of example in FIGS. 1 and 3, eachshutter 13 is rotatably mounted about its longitudinal axis 41 whichextends transversely with respect to the tank 10.

There will now be described by way of example various constructionspermitting the actuation of the shutters 13.

In accordance with FIG. 4A, each shutter 13 is articulated on twoparallel operating rods 45A, 458, common to all the shutters l3 andforming articulated parallelograms with these latter. These rods 45A,45B are in turn articulated on a common operating lever 46.

As will be readily understood, actuation of the lever 46 causes all theshutters 13 to pivot simultaneously about their axes 41.

A similar simultaneous operation could be obtained if the lever 46 andany element parallel to this lever, for example a shutter 13, were eachrespectively articulated at any two fixed points located on the sameparallel to the sides, forming a parallelogram with the said lever andthe said element.

According to H6. 45, at least one of the operating rods 45A, 458, therod 45A for example is replaced by a cord A which passes through eachshutter 13 and is provided on each side of the shutter with two fixedstops 48, in the same way as so-called Venetian blinds.

in accordance with the alternative form of construction shown in FIG.4C, at least one of the operating rods 45A, 45B, the rod 45B forexample, is replaced by a rack 245B comprising for each shutter 13 anangular slot 50 in which the shutter 13 is pivotally mounted in the sameway as a blade, the corresponding edge of the said shutter beingsharpened for that purpose.

This latter arrangement has the advantage of minimizing or eveneliminating the consequences of a possible jamming of crystals in thecontrol-rod system of the shutters 13.

As illustrated in FIG. 4D, the edges of the slot 50 in the rack 2458 areadvantageously bevelled.

According to various alternatives (not shown), the shutters 13 arereplaced by a single shutter, or in a more general way by valve orthrottling means of any kind.

According to the form of construction shown in FIG. 5, the tank iscylindrical and the throttling means which are associated with it arenot shutters as previously, but a variable-volume chamber 55, aninflatable chamber for example. This chamber is arranged in the centralzone of the tank 10, and, depending on its degree of inflation, itintercepts a more or less large portion of the transverse section ofthis tank.

As illustrated by FIG. 6, it is possible to associate a number of tanksI0 in parallel, each tank 10 comprising as previously its inlets and itsoutlets for liquor, MA, MB and A, 158 respectively.

In an association of this kind, some of the tanks 10 may not compriseany variable throttling means.

It has been assumed up to this point, when considering the applicationof the invention to a crystallization installation, that the liquor Awas a non-saturated liquor which is rich in dissolved product, heavierthan the liquor B which, derived from the crystallization circuit, isrelatively exhausted in dissolved product although it carries crystals.

It has also been assumed that these crystals were heavier than theliquors A and B.

The invention will also be applicable, in a more general way, to thecase in which the crystals to be sorted are lighter than the carrierfluid and the driving fluid employed, and would therefore have atendency to float. The fluid A being assumed for example to be lighterthan the fluid B, it is then only necessary to cause the crystals to beconveyed by the fluid A, to cause the latter to pass into the base ofthe separation chamber and to ensure at 148 an entering flow-rate offluid B greater than the outlet flow-rate at 158, so as to have a flowof fluid B from the top to the bottom, in opposition to the floatingmovement of the particles.

In all cases, the densities of the fluids A and B define a range ofdensities which excludes the density of the crystals to be sorted. Thedevices described above with reference to FIGS. 1 to 6 are staticdevices, that is to say devices which only comprise parts which arestationary, apart from the periods of adjustment.

There will now be described with reference to FIGS. 7 to 13 alternativeforms of dynamic construction, that is to say alternatives comprising amoving part for the creation of a force field independent of the fieldof normal gravity and most frequently greater than this latter.

To this end, a small wheel 60 is mounted so as to be freely rotatableinside a cylindrical chamber 61.

In accordance with the form of embodiment shown in FIGS. 7 to 10, theaxis of the chamber 61 and of the wheel 60 is horizontal.

This wheel comprises an axial conduit 62 partitioned by radial blades 63and provided externally, as can be more clearly seen from FIG. 8, withdriving blades 64 which are slightly curved in the same way as theblades of a Pelton wheel. Each blade 64 is parallel to the axis of thewheel and carries a portion 65 of an annular wall which is extended upto the vicinity of the adjacent blade 64, each blade 64 being itselfextended up to the vicinity of the chamber 61. These wall portions 65form with the axial conduit 62 an annular space 66 closed on theupstream side by a front plate 67, and open on the downstream side.

The wheel 60 occupies only a part of the internal space of the chamber61, the part of this internal space which is free forming the separationchamber V according to the invention proper, as will become apparentlater.

The mounting of the wheel 60 in the chamber 61 is effected by singlefluid bearings 68, 69 at each extremity of the said wheel, thesebearings being capable of permitting the passage of leakage.

In the axis of the axial conduit 62 of the wheel 60, the chamber 61, inaccordance with the form of embodiment shown in FIGS. 7 to 9, isprovided on the one hand with an axial supply pipe 1148 and on the otherhand with an axial outlet pipe 1158, this latter being located beyondthe separation chamber V or in this chamber.

In addition, at the level of the wheel 60, the chamber 61 is providedexternally with supply nozzles 114A arranged tangentially and uniformlydistributed around the periphery. These supply nozzles are preferablyconvergent and are arranged between the spaces defined by the fluidbearings 68 and 69.

Similarly, at its other extremity, the chamber 61 is provided externallywith outlet nozzles 1 15A, similar to the supply nozzles 114A, buthaving a larger cross-section.

Finally, the wheel 60 is provided axially, at the upstream extremity ofits axial conduit 62, with a hub 70 having the shape of a bullet.

The operation of this alternative form is as follows:

The liquor B carrying the crystals to be sorted is introduced to thepipe 1143, while the driving liquor A is introduced through the nozzles114A.

As previously, the flow passing out at USA is made less than the flowentering at 114A; and the flow passing out at 1 15B is made greater thanthe flow entering at 1148.

The liquor A injected by the nozzles 1 14A strikes the driving nozzlesof the wheel 60 and thereby causes the wheel to be set in rotation. Fromthis time onwards, due to the uniform distribution of the said nozzles,the wheel 60 is maintained floating in a balanced manner in the chamber61.

This latter being horizontal and the injection of the liquor A beingmade between the bearings 68 and 69, the wheel 60 is subjected only toslight axial reaction.

After contact with the driving blades 64 of the wheel 60, the liquor Ainjected by the nozzles 114A is directed by these blades towards theannular space 66 comprised between the axial conduit 62 and the portionsof wall 65, in the direction of the arrows 71 of FIG. 8. This liquor Athen leaves the wheel in rotation.

The liquor B which passes in at 114B, is directed towards the axialconduit 62 of the wheel 60 where the blades 63 also put this liquor intorotation.

At the outlet of the wheel 60 there are therefore in contact with eachother along a cylindrical interface 8', on the one hand the liquor B inthe axis of the chamber and on the other hand the liquor A locatedannularly round the said liquor B and rotating at the same speed as thislatter.

Due to the rotation of the liquor B, the crystals carried by this latterare subjected to a force field which is the more intense as this speedof rotation is high, that is to say the more intense as the speed ofrotation of the wheel 60 is high.

In this connection, the hub 70 has the purpose of deflecting slightlyfrom the axis of the wheel, those crystals which pass-in axially andwhich for this reason could escape from the effects of centrifugalforce.

By reason of this centrifugal force, the crystals have a tendency topass radially through the interface 8' in the direction of the arrow 140of FIG. 7, and by regulating the speed of rotation of the wheel 60 it ispossible to determine the diameter of the crystals which will besubjected to a sufi'icient amount of centrifugal force to passeffectively through this interface S, in counterflow with thecentripetal flow of liquor A resulting from the excess of the flowpassing-in at 114A with respect to the flow passing out at USA.

The regulation of this speed is effected by adjusting the flow-rate ofliquor injected through the nozzles lI4A, these nozzles being providedfor that purpose with the usual flow-regulating means (not shown in thedrawings).

At the downstream extremity of the chamber 61, the outlet nozzles 1 A ofthis latter evacuate a liquor into which have been transferred all thecrystals having a diameter greater than a pre-determined diametercorresponding to the speed of rotation of the wheel 60.

At the same time, the liquor from which these crystals have been removedis evacuated through the axial pipe 1158.

FIG. 10 relates to an alternative form in which the inlet nozzles 114Aare replaced by a diffuser 214A which is coupled to the chamber 61 alongan annular surface partitioned by fins 72. These fins are extended up tothe vicinity of the wheel 60 and the spaces between the fins can, atleast in certain cases, be closed for the purpose of regulating theflow-rate.

A similar arrangement may be adopted for the outlet nozzles USA.

In accordance with an alternative form (not shown), the chamber 61 isvertical or oblique, so that the wheel 60 is subjected to its ownweight.

In order to overcome the effect of this weight, the outer surface of theannular portions of wall 65 may be made frusto-conical in order that theforce resulting from the variations of pressure and speed of the liquoron the upstream and downstream sides of the wheel may substantiallybalance the weight of this latter.

As an alternative, the driving blades 64 may also be given an obliqueprofile on the axis of the wheel so as to balance the weight of thewheel.

In accordance with the alternative construction shown in FIG. 11, theinjection of liquor A into the chamber 61 is efi'ected by nozzles 214Aarranged axially at the upstream transverse extremity of this chamber,around the axial supply pipe 114B associated therewith, through whichthe liquor B passes-in. In this case, the wheel 60 is provided withdriving blades 164 which are oblique on its axis and which extendradially between its axial conduit 62 and an annular peripheral wall 165in the same way as the blades of a Francis turbine.

In addition, the axial conduit 62 is provided at its upstream extremitywith an extension 162 engaged in a fixed axial pipe 1148 and its axialhub is provided on its downstream face with a dished portion 76 servingas a supporting surface for a fixed locking rod 77. This latter iscarried on the chamber 61 by arms 78 and serves to compensate for theaxial thrust to which the wheel 60 is subjected due to the axialinjection of the liquor A.

At the same time, the outlet of the liquor A may be effected eitherthrough peripheral nozzles as previously, or through axial nozzles 215A,as shown, while the outlet of the liquor B is effected through an axialpipe 1 15B.

The operation of a construction of this kind is similar to thatdescribed above.

The arms 78 are preferably helicoidal to give a better adaptation ofthese arms to the flow of the liquor in which they are immersed, andextend into the axial pipe 1158 so as to form flow-straighteners bypreventing the rotation of the liquid in this pipe.

In the alternative forms of construction described with reference toFIGS. 7 to I], the wheel 60 is mounted freely rotating in the chamber61, and its rotation is effected by the injected liquor A, whichcorresponds to a certain loss of pressure in this liquor.

There will now be described with reference to FIGS. 12 and 13,alternative forms of construction according to which the wheel inaccordance with the invention is driven mechanically, which results in acertain application of pressure to the liquids in which it is immersed.

According to the alternative form shown in FIG. 12. this wheel is ashell 160 having the general shape of a hemisphere or a paraboloid ofrevolution, or of any surface comprised between the hemisphere and theparaboloid, driven in rotation by a shaft 80 which passes axiallythrough the chamber 161, with the interposition of a packing glandbearing 81. The shaft 80 is keyed on the output shaft of a motor,motor-reduction gear, motor speed-varying gear or the like (not shown).

On its concave face opposite to the shaft 80, the wheel 160 has twosuccessive layers of centrifugal blades 82, 83 extending respectivelybetween an axial inlet 84, 85 and a peripheral outlet 86, 87, the inlet85 forming a ring round the inlet 84.

Facing these inlets 84, 85, the fixed chamber 16] carries two concentricinlet pipes, an axial pipe 314A through which the liquor A isintroduced, and an annular pipe 314B through which the liquor B isintroduced.

The fixed chamber 161 further comprises outlet conduits 3158 and 315Aarranged annularly facing the outlets 86 and 85 of the centrifugalblades 82, 83 of the wheel 160.

According to this alternative form of construction, the liquors A and Bare put into contact as previously at the outlet of the wheel along asubstantially cylindrical interface S through which pass only thosecrystals having a sufficient diameter.

According to the alternative shown in FIG. 13, the supply of liquor A isefi'ected on the convex face of the wheel, this convex face beingprovided for that purpose with appropriate centrifugal blades, when sorequired.

At the same time, the inlet of the liquor B is effected as previously onthe concave face of the wheel 160, in the axial zone of this latter, andthis liquor is set in rotation, as previously, by centrifugal blades183.

The wheel also carries on its free peripheral edge, cylindricalextensions 85, 86, between which is developed the cylindrical interfaceS representing the contact surface of the liquors A and B at the outletof the wheel [60.

The operation of this alternative is similar to that of the precedingalternative construction.

It will of course be understood that the present invention is notlimited to the forms of embodiment described and shown, but covers anyalternative form of construction or of combination of their variouselements.

ln addition, its field of application is not limited only to thecrystallization installations of the type diagrammatically describedwith reference to FIG. 2, but extends to any type of crystallizationinstallation.

What] claim is:

l. A device for sorting crystals according to their size, comprising atank, means dividing said tank into two parts, said means permittingcrystals to pass from one part to the other and permitting liquor topass in the opposite direction, one of said parts having a fluid inletfor a carrier fluid and a fluid outlet, the other of said parts having afluid inlet for a driving fluid and a fluid outlet, and meansmaintaining the flow rate of fluid passing out of said other part lowerthan the flow rate of driving fluid passing into said other part wherebya portion of said driving fluid passes through said dividing means incountercurrent flow to a portion of said crystals, said dividing meansincluding an adjustable throttling means for altering the communicationbetween said two parts of said tank.

2. A device as claimed in claim I, said two parts being verticallysuperposed and said dividing means being substantially horizontal.

3. A device as claimed in claim 1, said throttling means comprising atleast one pivoted shutter extending across said tank.

4. A device as claimed in claim 3, at least one of the edges of saidshutter being pivotally mounted in the manner of a knife blade in a slotformed in an operating rack member.

5. A device as claimed in claim 3, there being a plurality of saidshutters actuated by a common control.

6. A device as claimed in claim 1, said inlet of said one part of saidtank being smaller than said outlet of said one part of said tank, saidinlet of said other part of said tank being larger than said outlet ofsaid other part of said tank.

7. A method of sorting crystals according to their size, comprisingestablishing a pair of chambers separated by means through which fluidcan pass in one direction and crystals can pass in the oppositedirection, introducing carrier fluid containing crystals suspendedtherein into one chamber, withdrawing fluid from said one chamber at aflow rate greater than the rate of introduction of fluid into said onechamber, in-

tr ucin drivin flui it theot rs idchamber,and wfidraw mg drimg :2! romsaid at er chamber at a rate of flow less than the rate of flow ofdriving fluid into said other chamber whereby fluid passes from saidother chamber to said one chamber in countercurrent with crystalspassing from said one chamber to said other chamber, said fluids havingdifferent densities, the density of said crystals lying outside therange of densities of said fluids.

8. A method as claimed in claim 7, the density of said driving fluidbeing higher than the density of said carrier fluid.

# i O I

1. A device for sorting crystals according to their size, comprising atank, means dividing said tank into two parts, said means permittingcrystals to pass from one part to the other and permitting liquor topass in the opposite direction, one of said parts having a fluid inletfor a carrier fluid and a fluid outlet, the other of said parts having afluid inlet for a driving fluid and a fluid outlet, and meansmaintaining the flow rate of fluid passing out of said other part lowerthan the flow rate of driving fluid passing into said other part wherebya portion of said driving fluid passes through said dividing means incountercurrent flow to a portion of said crystals, said dividing meansincluding an adjustable throttling means for altering the communicationbetween said two parts of said tank.
 2. A device as claimed in claim 1,said two parts being vertically superposed and said dividing means beingsubstantially horizontal.
 3. A device as claimed in claim 1, saidthrottling means comprising at least one pivoted shutter extendingacross said tank.
 4. A device as claimed in claim 3, at least one of theedges of said shutter being pivotally mounted in the manner of a knifeblade in a slot formed in an operating rack member.
 5. A device asclaimed in claim 3, there being a plurality of said shutters actuated bya common control.
 6. A device as claimed in claim 1, said inlet of saidone part of said tank being smaller than said outlet of said one part ofsaid tank, said inlet of said other part of said tank being larger thansaid outlet of said other part of said tank.
 7. A method of sortingcrystals according to their size, comprising establishing a pair ofchambers separated by means through which fluid can pass in onedirection and crystals can pass in the opposite direction, introducingcarrier fluid containing crystals suspended therein into one chamber,withdrawing fluid from said one chamber at a flow rate greater than therate of introduction of fluid into said one chamber, introducing drivingfluid into the other said chamber, and withdrawing driving fluid fromsaid other chamber at a rate of flow less than the rate of flow ofdriving fluid into said other chamber whereby fluid passes from saidother chamber to said one chamber in countercurrent with crystalspassing from said one chamber to said other chamber, said fluids havingdifferent densities, the density of said crystals lying outside therange of densities of said fluids.
 8. A method as claimed in claim 7,the density of said driving fluid being higher than the density of saidcarrier fluid.